This Project will focus on the factors that control the replication of smooth muscle cells which form the intima, 4 weeks after balloon catheter injury. Recent data from this laboratory has shown that in vivo these cells only respond weakly to FGF2 but other FGF-induced events such as expression of uPA and activation of the extra-cellular signal kinases pathway (ERKs) are induced. Further if these intimas are re-injured with an angioplasty catheter then significant SMC replication is induced. The aims are to understand what is responsible for the intimal SMC replication seen after re-injury and why FGF2, while able to stimulate several SMC responses, is not able to induce significant intimal replication. To attain these, we plan to examine the expression of FGF1, PDGF B-chain, PDGF A-chain, while the role of platelets and thrombin on SMC replication will be examined by inhibiting these factors. The expression of potential SMC inhibitors with the intimal SMC blocked with specific inhibitors. The role of FGF1 and FGF2 on intimal SMC replication will be assessed using knock-out mice. The carotid arteries of these mice will be injured and the replication of SMC and growth of intimal lesions determined. To insure that the deletion of one FGF is compensated by over expression of another FGF, we will also use FGFR1 KO animals. This gene deletion is lethal and so chimeric mice will be made and using a phenotype marker for the FGFR-/- cells. determine the importance of FGFG1 stimulation in development of arteries and in the response of their SMC to injury. We have shown that the MAP kinase pathway is activated by the addition of FGF2 in intimal lesions and yet these cells show a weak ability to replicate. We will examine the duration of activation of this pathway in injured arteries and determine if inactivation is caused by the mitogen-activate kinase phosphatases (MKP-1) which is expressed by intimal SMC. Finally, we plan to determine if inhibitors of cell replication, namely cdk-activating kinase inhibitors, p21 and p27 and the stress- activated protein kinase pathway (SAPKs) are active in the injured arteries and after re-injury. Both these factors have the potential to inhibit cell replication. Collectively these studies should provide important data on the factors and pathways that are important for permitting SMC to replicate.